Geo-pressured aquifers are water reservoirs containing water and natural gas and exist at pressures substantially higher than hydrostatic pressure and when in communication with a well bore will flow water to the surface of the ground in artesian fashion.
Natural gas may be present in geo-pressured aquifers in the form of (1) gas dissolved in the water and also in the form of (2) a free-gas phase dispersed with water within the sand pores. An additional form of natural gas may exist in depleted and non-commercial geo-pressured gas reservoirs where (3) a free-gas phase is present within the sand pores above and separate from the water.
Our prior application Ser. No. 689,621, now U.S. Pat. No. 4,040,487, was directed to producing water from wells completed in geo-pressured aquifers so as to maximize the recovery of natural gas by producing water from an aquifer under aquifer pressure so as to lower the pressure in the aquifer sufficiently to allow a portion of the gas to be released from solution whereby the released gas would migrate more freely than the water to the well and be produced and the gas recovered at the surface. However, the gas released from the water in such a method may flow, not to the producing wells, but to a trap in the aquifer to form a free-gas phase in the trap or to enlarge a previously formed free-gas phase existing in the trap.
The present invention is directed to a method of maximizing gas yield from geo-pressured aquifers by producing additional gas trapped in the trap which also has the advantage of further reducing the pressure in the aquifer and thereby releasing additional gas for production.